This invention relates to the direct injection of selected thermal-infrared (IR) wavelength radiation or energy into targeted entities for a wide range of heating, processing, or treatment purposes. As will be described below, these purposes may include heating, raising or maintaining the temperature of articles, or stimulating a target item in a range of different industrial, medical, consumer, or commercial circumstances. The methods and system described herein are especially applicable to operations that require or benefit from the ability to irradiate at specifically selected wavelengths or to pulse or inject the radiation. The invention is particularly advantageous when the target is moving at higher speeds and in a non-contact environment with the target. The invention provides for an infrared system of selected narrow wavelengths which is highly programmable for a wide range of end applications. The invention teaches a new and novel type of infrared irradiation system which is comprised of engineered arrays of most preferably a new class of narrow wavelength solid-state radiation emitting devices (REDs), one variant of which will be specifically referenced later in this document.
More specifically, this invention is directed to a novel and efficient way of injecting an optimal wavelength of infrared radiation into a target for the purpose of, in some way, affecting the target's temperature. To cite a small sampling of examples, the “target” for the infrared injection may be from a wide variety of items ranging from individual components in a manufacturing operation, to a region of treatment on a continuous coil of material, to food in a cooking process, or to human patients in a medical treatment environment.
Though the specific embodiment of the invention described hereafter is an example that relates particularly to a plastic bottle preform reheat operation, the concepts contained within also apply to many other noted scenarios. It also applies to single-stage plastic bottle blowing operations wherein the injection-molding operation is performed serially, just prior to the blow-molding operation. In this deployment, for example, the methods and apparatus of the subject invention offer similar advantages over the known art, but would employ different sensing and controls to deal with the variation in initial temperature at the entrance to the reheat section of the process.
In general, an ideal infrared heating system optimally raises the temperature of a target with the least energy consumption. Such a system may comprise a device that can directly convert its electrical power input to a radiant electromagnetic energy output, with the chosen single or narrow band wavelengths that are aimed at a target, such that the energy comprising the irradiation is partially or fully absorbed by the target and converted to heat. The more efficiently the electrical input is converted to radiant electromagnetic output, the more efficiently the system can perform. The more efficiently the radiant electromagnetic waves are aimed to expose only the desired areas on the target, the more efficiently the system will accomplish its work. The radiation emitting device chosen for use should have an instant “on” and instant “off” characteristic such that when the target is not being irradiated, neither the input nor the-output energy is wasted. The more efficiently the exposed target absorbs the radiant electromagnetic energy to directly convert it to heat, the more efficiently the system can function. For an optimal system, care must be taken to properly select so that the set of system output wavelengths matches the absorptive characteristic of the target. These wavelengths likely will be chosen differently for different targeted applications of the invention to best suit the different absorption characteristics of different materials as well as to suit different desired results.
In contrast, it is well known in the art and industry to use a range of different types of radiant heating systems for a wide range of processes and treatments. Technologies that have been available previously for such purposes produce a relatively broad band spectrum of emitted radiant electromagnetic energy. They may be referred to as infrared heating, treatment, or processing systems whereas, in actual fact, they often produce radiant energy well outside the infrared spectrum.
The infrared portion of the spectrum is generally divided into three wavelength classifications. These are generally categorized as near-infrared, middle-infrared, and long-infrared wavelengths bands. While exact cutoff points are not clearly established for these general regions, it is generally accepted that the near-infrared region spans the range between visible light and 1.5 micrometers. The middle-infrared region spans the range from 1.5 to 5 micrometers. The long-wave-infrared region is generally thought to be between 5 and 14 micrometers and beyond.
The radiant infrared sources that have been used in industrial, commercial, and medical, heating treatment or process equipment previously produce a broad band of wavelengths which are rarely limited to one section of the infrared spectrum. Although their broad band output may peak in a particular range of the infrared spectrum, they typically have an output tail which extends well into adjacent regions.
As an example, quartz infrared heating lamps, which are well known in the art and are used for various process heating operations, will often produce a peak output in the 0.8 to 1 micrometer range. Although the output may peak between 0.8 and 1 micrometers, these lamps have substantial output in a wide continuous set of wavelength bands from the ultraviolet (UV) through the visible and out to about 3.5 micrometers in the middle-infrared. Clearly, although the peak output of a quartz lamp is in the near-infrared range, there is substantial output in both the visible range and in the mid-infrared ranges. It is, therefore, not possible with the existing broad spectrum infrared sources to be selective as to the preferred wavelength or wavelengths that would be the most desired for any given heating, processing or treatment application. It is inherently a wide spectrum treatment or process and has been widely used because there have not been practical alternatives before the present invention. The primary temperature rise in many targets is due to absorption of thermal IR energy at one or more narrow bands of wavelengths. Thus, much of the broadband IR energy output is wasted.
Nonetheless, quartz infrared lights are widely used in industry for both the discrete components and the continuous material processing industries. A variety of methodologies would typically be used to help direct the emission from the quartz lamps onto the target under process including a variety of reflector-types. Regardless of how the energy is focused onto the target, the quartz lamps are typically energized continuously. This is true whether the target under process is a continuously produced article or discrete components. The reason for this is primarily due to the relatively slow thermal response time of quartz lamps which typically measure on the order of seconds.
An area of specific need for improved energy injection relates to blow molding operations. More specifically, plastic bottle stretch blow-molding systems thermally condition preforms prior to stretch blow molding operations. One aspect of this process is known in the art as a reheat operation. In a reheat operation, preforms that have been formed by way of an injection molding or compression molding process are allowed to thermally stabilize to room temperature. At a later time, the preforms are fed into a stretch blow molding system, an early stage of which heats up the preforms to a temperature wherein the thermoplastic preform material is at a temperature optimized for subsequent blow-molding operations. This condition is met while the preforms are being transported through a heating section along the path to the blow molding section of the machine. In the blow molding section, the preforms are first mechanically stretched and then blown into vessels or containers of larger volume.
Energy consumption costs make up a large percentage of the cost of a finished article that is manufactured using blow molding operations. More specifically, the amount of energy required with the heretofore state-of-the-art technology to heat up or thermally condition Polyethylene Terephthalate (PET) preforms from ambient temperature to 105° C. in the reheat section of a stretch blow molding machine is quite substantial. From all manufacturing efficiently measures, it will be clearly advantageous from both an economic and an environmental standpoint to reduce the energy consumption rate associated with the operation of the thermal conditioning section of stretch blow molding systems.
U.S. Pat. No. 5,322,651 describes an improvement in the method for thermally treating thermoplastic preforms. In this patent, the conventional practice of using broadband infrared (IR) radiation heating for the thermal treatment of plastic preforms is described. Quoting text from this patent, “In comparison with other heating or thermal treatment methods such as convection and conduction, and considering the low thermal conductivity of the material, heating using infrared radiation gives advantageous output and allows increased production rates.”
The particular improvement to the state-of-the-art described in this patent relates to the manner in which excess energy emitted during IR heating of the preforms is managed. In particular, this patent concerns itself with energy emitted during the heating process that ultimately (through absorption in places other than the preforms, conduction, and then convection) results in an increase in the air temperature in the oven volume surrounding the transported preforms. Convection heating of the preforms caused by hot air flow has proven to result in non-uniform heating of the preforms and, thus, has a deleterious effect on the manufacturing operation. U.S. Pat. No. 5,322,651 describes a method of counteracting the effects of the unintended heating of the air flow surrounding the preforms during IR heating operations.
As might be expected, the transfer of thermal energy from historical state-of-the-art IR heating elements and systems to the targeted preforms is not a completely efficient process. Ideally, 100% of the energy consumed to thermally condition preforms would end up within the volume of the preforms in the form of heat energy. Although it was not specifically mentioned in the above referenced patent, typical conversion efficiency values (energy into transported preforms/energy consumed by IR heating elements) in the range between 5% and 10% are claimed by the current state-of-the-art blow molding machines. Any improvement to the method or means associated with the infrared heating of preforms that improves the conversion efficiency values would be very advantageous and represents a substantial reduction in energy costs for the user of the stretch blow forming machines.
There are many factors that work together to establish the energy conversion efficiency performance of the IR heating elements and systems used in the current state-of-the-art blow molding machines. As noted, conventional thermoplastic preforms, such as PET preforms, are heated to a temperature of about 105° C. This is typically accomplished in state-of-the-art blow molding machines using commercially available broadband quartz infrared lamps. In high-speed/high-production machines these often take the form of large banks of very high wattage bulbs. The composite energy draw of all the banks of quartz lamps becomes a huge current draw amounting to many hundreds of kilowatts on the fastest machines. Two factors associated with these types of IR heating elements that have an effect on the overall energy conversion efficiency performance of the overall heating system are the color temperature of the lamp filament and the optical transmission properties of the filament bulb.
Another factor that has a significant impact on the overall energy conversion performance of the thermal conditioning subsystems of the current state-of-the-art blow molding machines is the flux control or lensing measures used to direct the IR radiation emitted by the heating elements into the volume of the preforms being transported through the system. In most state-of-the-art blow molding machines, some measures to direct the IR radiant flux emitted by quartz lamps into the volume of the preforms are being deployed. In particular, metallized reflectors work well to reduce the amount of emitted IR radiation that is wasted in these systems.
Still another factor that has an impact on the energy conversion efficiency performance of the IR heating subsystem is the degree to which input energy to the typically stationary IR heating elements is synchronized to the movement of the preforms moving through the heating system. More specifically, if a fixed amount of input energy is continuously consumed by a stationary IR heating element, even at times when there are no preforms in the immediate vicinity of the heater due to continuous preform movement through the system, the energy conversion efficiency performance of the systems is obviously not optimized. In practice, the slow physical response times of commercial quartz lamps and the relatively fast preform transfer speeds of state-of-the-art blow molding machines precludes any attempt of successfully modulating the lamp input power to synchronize it with discrete part movement and, thus, achieve an improvement in overall energy conversion efficiency performance.
U.S. Pat. Nos. 5,925,710, 6,022,920, and 6,503,586 B1 all describe similar methods to increase the percentage of energy emitted by IR lamps that is absorbed by transported preforms used in a blow molding process. All of these patents describe, in varying amounts of detail, the general practice in state-of-the-art reheat blow molding machines to use quartz lamps as the IR heating elements. In a reheat blow molding process, preforms that have previously been injection molded and allowed to stabilize to room temperature are reheated to blowing temperatures just prior to blow molding operations. These above reference patents describe how polymers in general, and PET in particular, can be heated more efficiently by IR absorption than is possible using conduction or convection means. These patents document in figures the measured absorption coefficient of PET as a function of wavelength. Numerous strong molecular absorption bands occur in PET, primarily in IR wavelength bands above 1.6 micrometer. Quartz lamps are known to emit radiation across a broad spectrum, the exact emission spectrum being determined by the filament temperature as defined by Planck's Law.
As used in existing state-of-the-art blow molding machines, quartz lamps are operated at a filament temperature of around 3000° K. At this temperature, the lamps have a peak radiant emission at around 0.8 micrometer. However, since the emission is a blackbody type emission, as it is known in the art, the quartz filament emits a continuous spectrum of energy from X-ray to very long IR. At 3000° K., the emission rises through the visible region, peaks at 0.8 micrometer, and then gradually decreases as it begins to overlap the regions of significant PET absorption starting at around 1.6 micrometer.
What is not described in any of these patents is the effect that the quartz bulb has on the emitted spectrum of the lamp. The quartz material used to fabricate the bulb of commercial quartz lamps has an upper transmission limit of approximately 3.5 micrometer. Beyond this wavelength, any energy emitted by the enclosed filament is, for the most part, absorbed by the quartz glass sheath that encloses the filament and is therefore not directly available for preform heating.
For the reasons outlined above, in existing state-of-the-art blow molding machines that use quartz lamps to reheat PET preforms to blowing temperatures, the range of absorptive heating takes place between 1 micrometer and 3.5 micrometer. The group of patents referenced above (U.S. Pat Nos. 5,925,710, 6,022,920, and 6,503,586 B1) all describe different method and means for changing the natural absorption properties of the preform, thus improving the overall energy conversion efficiency performance of the reheat process. In all of these patents, foreign materials are described as being added to the PET preform stock for the sole purpose of increasing the absorption coefficient of the mixture. These described methods and means are intended to effect the materials optical absorption properties in the range from the near IR around 0.8 micrometer out to 3.5 micrometer. While being a viable means of increasing the overall energy conversion efficiency performance of the reheat process, the change in the absorption property of the preforms that is so beneficial in reducing the manufacturing costs of the container also has a deleterious effect on the appearance of the finished container. A reduction in the optical clarity of the container, sometimes referred to as a hazing of the container, acts to make this general approach a non-optimal solution to this manufacturing challenge.
U.S. Pat. No. 5,206,039 describes a one-stage injection molding/blow molding system consisting of an improved means of conditioning and transporting preforms from the injection stage to the blowing stage of the process. In this patent, the independent operation of an injection molding machine and a blow molding machine, each adding a significant amount of energy into the process of thermally conditioning the thermoplastic material, is described as wasteful. This patent teaches that using a single-stage manufacturing process reduces both overall energy consumption rates and manufacturing costs. This reduction in energy consumption comes primarily from the fact that most of the thermal energy required to enable the blow molding operation is retained by the preform following the injection molding stage. More specifically, in a one-stage process as described in the '039 patent, the preform is not allowed to stabilize to room temperature after the injection molding process. Rather, the preforms move directly from the injection molding stage to a thermal conditioning section and then on to the blow molding section.
The thermal conditioning section described in the '039 patent has the properties of being able to add smaller amounts of thermal energy as well as subjecting the preforms to controlled stabilization periods. This differs from the requirements of a thermal conditioning section in the 2-stage process of a reheat blow-molding machine wherein large amounts of energy are required to heat the preforms to the blowing temperature. Though the operation of single-stage injection molding/blow molding machines are known in the art, finished container quality problems persist for these machines. These quality problems are linked to preform-to-preform temperature variations as the stream of preforms enters the blowing stage. Despite the advances described in the '039 patent, using heretofore state-of-the-art IR heating and temperature sensing means and methods, the process of thermally conditioning preforms shortly after they have been removed from an injection molding process still results in preforms of varying thermal content entering the blowing stage. The variations in thermal content of the entering preforms result in finished containers of varying properties and quality. Inefficiencies in the ability to custom tune the IR heating process on a preform-to-preform basis results in manufacturers opting to use a reheat blow molding method to achieve required quality levels. For this reason, for the highest production applications, the industry's reliance on reheat methods persists. Also, because preforms are often manufactured by a commercial converter and sold to an end user who will blow and fill the containers, the re-heat process continues to be popular.
The prospect of generally improving the efficiency and/or functionality of the IR heating section of blow molding machines is clearly advantageous from both an operating cost as well as product quality perspective. Though several attempts have been made to render improvements in the state-of-the-art IR heating subsystems, clear deficiencies still persist. Through the introduction of novel IR heating elements and methods, it is the intention of the present invention to overcome these deficiencies.
In the solid state electronics realm, solid-state emitters or LEDs are well known in the art. Photon or flux emitters of this type are known to be commercially available and to operate at various wavelengths from the ultraviolet (UV) through the near-infrared. LEDs are constructed out of suitably N- and P-doped semiconductor material. A volume of semiconductor material suitably processed to contain a P-doped region placed in direct contact with an N-doped region of the same material is given the generic name of diode. Diodes have many important electrical and photoelectrical properties as is well known in the art. For example, it is well known within the art that, at the physical interface between an N-doped region and a P-doped region of a formed semiconductor diode, a characteristic bandgap exists in the material. This bandgap relates to the difference in energy level of an electron located in the conduction band in the N-region to the energy level of an electron in a lower available P-region orbital. When electrons are induced to flow across the PN-junction, electron energy level transitions from N-region conduction orbitals to lower P-region orbitals begin to happen resulting in the emission of a photon for each such electron transition. The exact energy level or, alternately, wavelength of the emitted photon corresponds to the drop in energy of the conducted electron.
In short, LEDs operate as direct current-to-photon emitters. Unlike filament or other blackbody type emitters, there is no requirement to transfer input energy into the intermediate form of heat prior to being able to extract an output photon. Because of this direct current-to-photon behavior, LEDs have the property of being extremely fast acting. LEDs have been used in numerous applications requiring the generation of extremely high pulse rate UV, visible, and/or near IR light. One specific application wherein the high pulse rate property of LEDs has been particularly useful is in automated discrete part vision sensing applications, where the visible or near infrared light is used to form a lens focused image which is then inspected in a computer.
Unlike filament-based sources, LEDs emit over a relatively limited wavelength range corresponding to the specific bandgap of the semiconductor material being used. This property of LEDs has been particularly useful in applications wherein wavelength-selective operations such as component illumination, status indication, or optical communication are required. More recently, large clusters of LEDs have been used for larger scale forms of visible illumination or even for signaling lights such as automotive tail lights or traffic signal lights.